Previous studies from our laboratory indicate that ovine placental lactogen is a potent growth-promoting factor which stimulates somatomedin-C production in hypophysectomized immature rats and intermediary metabolism in pregnant sheep. As an extenson of these investigations, we now propose to examine 1) the effects of ovine placental lactogen on somatomedin-C production and intermediary metabolism in the sheep fetus and compare these effects to those of growth hormone and prolactin and 2) to study the relative potenciesssssof ovine placental lactogen, growth hormone and prolacting in stimulating the hepatic uptake of neutral amino acids and monosaccharides and the incorporation of amino acids into heaptic proteins in the rat fetus. Other investigations from our laboratory have demonstrated that the secretion of human placental lactogen in vitro is stimulated in a dose-dependent manner by an as yet unidentified heat stable protein in prgenancy serum which has a molecular weight of 10-50,000 daltons and which stimulates placental membrane phospholipase activity. As an extension of these studies, we now propose to purify and characterize this serum protein, study the mechanism by which it exerts its stimulatory activity, develop a radioimmunoassay for its detection in biological fluids and determine its concentration in normal pregnancy and in pregnancies associated with aberrations in human placental lactogen secretion, such as diabetes mellitus and pre-eclampsia. Since the biologic actions of placenta lactogen in the fetus are unknown and the factors regulating its secretion are poorly understood, these investigations should provide consierable insight into the physiology of placental lactogen and into the pathophysiology of those conditions associated with abnormal human placental lactogen secretion.